Scintiscanning demonstration of thymoma: comparative study on scintiscans using 201Tl, 67Ga and 75Se.

Thymus scintigraphy was performed using 201Tl-chloride, 67Ga-citrate and 75Se-selenomethionine on 30 thymoma patients with or without myasthenia gravis. Mass negativity was observed in 6 out of 17 (35.3 per cent) and 3 out of 13 cases (23.1 per cent), respectively. A rate of 70 per cent (21 cases out of 30) of mass positivity was observed by thymus scan using 201Tl. With regard to the relation between thymus scan and cell type, 201Tl-scan exhibited a high rate of mass positivity, regardless of the cell type while the 75Se-scan showed a trend toward mass positivity in epithelial cell predominant cases. With 201Tl, mass positivity was observed when the CPM/g ratio for tumors and blood exceeded 3.0. This trend can serve as an index for the suitability of supplementary chemo- and radiotherapies, as well as for prognosis in cases of relapse, and in those for whom excision was not complete.